1. Technical Field of the Invention
This invention relates to protective envelopes and, particularly, to a new method for the manufacture of jackets for flexible magnetic disks, and the new disk jacket.
2. Description of the Prior Art
A flexible magnetic disk jacket encloses and protects a magnetic disk and is inserted along with the disk into a so-called disk drive which is connected to a computer system. The disk drive includes a read/write magnetic head which contacts the magnetic disk through openings in the jacket and either magnetically records information supplied by a computer system onto the disk or magnetically reads information from the disk and supplies such information to the computer system.
In order that information recorded upon a particular magnetic disk be readable in a variety of disk drives produced by various manufactures, certain standards for disk jacket flatness and dimensions have been developed. One such standard is the American National Standards Institute (ANSI) specification X3B8/78-145. Jackets which are not flat within allowable limits may be difficult to insert into the disk and also may cause data reliability problems due to head-to-disk contact instability and/or separation.
The present industry-accepted method of manufacturing a disk jacket is disclosed in U.S. Pat. No. 4,038,693, issued to Huffine et al., on July 26, 1977, and U.S. Pat. No. 4,263,634, issued to Chenoweth et al., on Apr. 21, 1981. These patents illustrate a disk jacket formed from a rectangular perimeter cut sheet which includes three envelope-type flaps extending from the three edges of one-half of the rectangular sheet. The centerline of the sheet is heated and folded to define top and bottom panels of the jacket and the two flaps adjacent this fold are in turn folded over the top panel and secured with an adhesive or by thermal bonding techniques or ultrasonic welding to form a pocket. The magnetic disk is inserted into this pocket and the flap opposite the initial centerline fold is folded over and likewise secured to contain the magnetic disk and form a completed jacket.
Although folded jackets may be produced rapidly by drawing on carton or envelope technology, problems associated with jackets produced in this manner are that the gap between the top and bottom panels and the thickness of the jacket are not uniform either because the edges of the jacket are pressed tightly together adjacent the folded flaps or because of distortion caused by prefold heating of the jacket material. Since the top and bottom panels are adjacent one another and forced together at three sides of the perimeter, there is a danger that the disk may be pinched between the panels and prevented from rotating freely if a uniform gap between these panels is not maintained. This may result in greatly increased rotational torque or destruction of the magnetic disk.
U.S. Pat. No. 3,864,755, issued to Hargis on Feb. 4, 1975, has attempted to overcome these problems by providing a disk jacket which has a relatively rigid, flat back cover and a relatively thin front cover which is thermoformed over the disk and bonded to the flat back cover. Nonwoven synthetic fiber wiper layers are interposed between the surfaces of the disk and the front and back covers to clean the disk and prevent the edge of the disk from becoming wedged in the junction of the front and back covers. A similar construction is shown in U.S. Pat. No. 3,668,658, issued to Flores et al., on June 6, 1972, in which the jacket is a composite of three sheets which include a central gasket layer surrounding the magnetic disk and adhesively attached to flat side panels.
While composite layer types of jackets are an improvement over folded jackets in that a uniform gap is provided in which the disk may freely rotate and the laminated structure increased rigidity and reduces distortion, they have not proven entirely successful in preventing the disk from becoming wedged in the junctions of the layers and have proven expensive because additional production steps are required to cut the layers and align the separate layers.
It would be desirable, therefore, to produce a jacket by folding a single sheet of material which provided a laminated structure and a definite, uniform gap for the disk between the outer jacket panels. Such a jacket would allow high production volumes and reduce the possibility of jacket distortion and consequential high disk rotational torque.